Embodiments of the present invention relate to a method and system for determining the torque induced in a rotating shaft. In particular the invention relates to a method and system for determining the torque induced in a shaft in a turbine engine.
It is often useful to be able to measure the torque induced in a rotating shaft such as a shaft in a turbine engine. The torque induced in a shaft in a turbine engine is related to the power produced by the engine so a measurement of the torque may provide an indication of the performance of an engine. Such measurements may be useful during the testing and development of an engine or during the use of an engine for control or health monitoring purposes.
The torque T induced in a rotating shaft is given byT=εθ
Where ε is the torsional stiffness of the shaft and θ is the angle of the twist induced in the shaft.
Methods of measuring the angle of twist over a range of operating conditions are well known in the art. Apparatus suitable for making such measurements, such as multipole sensors and strain gauges, are also well known.
The torsional stiffness of a shaft is a measure of the resistance of the shaft to being twisted. It can be difficult to obtain an instantaneous value of the torsional stiffness of a shaft in a turbine engine because the mechanical properties of the shaft depend on a number of factors including operating conditions such as temperature and pressure and the history of use of the shaft. In a turbine engine the operating conditions may vary along the length of the shaft so the stiffness of the shaft may also vary along the length of the shaft. This makes it difficult to compute an accurate model which can be used to determine an instantaneous value of the stiffness while the shaft is in use.